1. Field of the Invention
The present invention relates to an internal combustion engine capable of operating on auto-ignition combustion, and a system for and a method of controlling fuel delivery in a fuel injection system capable of performing a multiple injection wherein a main injection event and a trigger injection event take place in this order in one cycle.
2. Description of Related Art
When certain conditions are met within a charge of lean air/fuel mixture during low load operation, auto-ignition can occur wherein bulk combustion takes place initiated simultaneously from many ignition sites within the charge, resulting in very stable power output, very clean combustion and high thermal efficiency. NOx emission produced in controlled auto-ignition combustion is extremely low. In controlled auto-ignition combustion where the combustion is uniformly distributed throughout the charge from many ignition sites, the burnt gas temperature is substantially homogeneous with much lower local temperature values resulting in very low NOx emission.
Auto-ignition combustion at low speeds with low or middle load and spark-ignition combustion at high speeds with high or full load result in enhanced fuel consumption rate and reduced NOx emission at low speeds with low or middle load and high power output at high speeds with high or full load.
An auto-ignition, which is induced by heating fuel and significantly increasing the compression ratio, in four-stroke gasoline engine is described in U.S. Pat. No. 5,535,716, which claims priority of Japanese patent application No. 6-150487 that was laid open as JP-A 7-332141 on Dec. 22, 1995. Gasoline fuel is injected inside the intake port a considerable amount of time before the intake valve is open so that the mixture of air and gasoline in the intake port is sufficiently heated before entering the combustion chamber. The mixture is ignited by auto-ignition performed at high pressure. Since fuel sprayed within the intake port is completely evaporated before entering the combustion chamber, reliable auto-ignition is achieved. The compression ratio ranges from about 14 to about 20. Use of a compression ratio of 17.7 is described as the most preferred implementation. Injection is performed during a predetermined period from 10 degrees of crank angle before the intake valve is closed to 110 degrees of crank angle before the intake valve is opened.
In this known auto-ignition internal combustion engine, beginning of burning is governed by speed of cool oxidation reaction of gasoline under conditions when temperature and pressure rise due to compression by piston. Thus, it is within very narrow operation range that auto-ignition combustion is accomplished wherein beginning of burning occurs around TDC of compression stroke.
JP-A 11-72038 discloses a diesel engine having a fuel injection system capable of performing a split injection wherein fuel quantity for first injection is kept lower than or as low as 30% of total fuel quantity so that the remainder is set aside for second fuel injection at TDC of compression stroke.
According to this known technique, relatively large percent of the total fuel quantity is sprayed at around TDC of compression stroke. Sufficient mixing of air and fuel cannot be expected if total fuel quantity becomes great. Under this condition, burnt gas temperature is highly heterogeneous with very high local temperature values creating high NOx emission. Besides, beginning of burning is not controllably adjusted toward an appropriate crank angle around TDC of compression stroke against varying operating conditions, making it difficult to extend operation range where auto-ignition combustion can be accomplished. Thus, expected improvement in fuel consumption rate and emission performance cannot be made.
JP-A 10-252512 discloses an internal combustion engine having two fuel injectors, namely, a port fuel injector in communication with an intake port and a cylinder fuel injector in communication with a combustion chamber. At light load below a predetermined level, cylinder injection is suspended and total fuel quantity is sprayed into the intake port from the port fuel injector. Besides, intake and exhaust valves are adjusted to vary exhaust gas retaining duration to control cylinder temperature to provide conditions for auto-ignition. At load exceeding the predetermined level, the port fuel injector sprays fuel quantity corresponding to the predetermined level of load, and the cylinder fuel injector sprays insufficiency of total fuel quantity at around TDC of compression stroke.
According to this known technique, fuel quantity for injection by the cylinder fuel injector increases linearly as load request increases at high load exceeding the predetermined level. Sufficient mixing of air and fuel cannot be expected if total fuel quantity becomes great. Under this condition, burnt gas temperature is highly heterogeneous with very high local temperature values creating high NOx emission. Besides, beginning of burning is not controllably adjusted toward an appropriate crank angle around TDC of compression stroke against varying operating conditions, making it difficult to extend operation range where auto-ignition combustion can be accomplished. Thus, expected improvement in fuel consumption rate and emission performance cannot be made.
Several attempts are being made to enhance fuel injection capabilities to extend operating conditions at which auto-ignition combustion is accomplished. One such method is known as multiple or divided injection including split injection. Split injection consists of a first injection event separated from a second injection event by a delay.
It is an object of the present invention to provide a system and method for enhancing engine operation on auto-ignition combustion of fuel at extended operating conditions.
It is another object of the present invention to provide an internal combustion engine with a fuel injection system capable of performing enhanced fuel injection that enhances engine operation on auto-ignition combustion of fuel at extended operating conditions.
In accordance with one aspect of the present invention, there is provided an internal combustion engine comprising:
at least one cylinder for receiving a piston to define a combustion chamber;
an engine controller;
a fuel injection system having a fuel injector for delivering fuel to the combustion chamber; and
a computer readable storage medium having information stored thereon representing instructions executable by the engine controller to enhance engine operation on auto-ignition combustion, wherein the engine controller is capable of controlling the fuel injection system to perform a multiple injection wherein a main injection event and a trigger injection event take place in this order in one cycle, and wherein the computer readable storage medium includes instructions for operating the engine controller to:
determine operating conditions; and
determine fuel quantity and injection timing for at least one of main and trigger injections corresponding to the operating conditions to enable the multiple injection to govern beginning of burning (BOB).